Augmented thrust pulse jet pump or motor and method of creating augmented thrust or suction



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AUGMENTED THRUST PULSE JET PUMP OR MOTOR AND METHOD OF CREATING AUGMENTED THRUST OR SUCTION Filed June G, 1950 l1 Sheets-Sheet 3 1N VEN TOR. my E. /x/a web@ u( m /M nrrafavsy 2,659,202 HOD F. E. NULL Nov. 17, 1953 AUGMENTED THRUST PULSE JET PUMP OR MOTOR AND MET OF CREATING AUGMENTED THRUST OR SUCTION ll Sheets-Sheet 4 Filed June 6, 1950 INVENTOR. FAV E. /VM

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AUGMENTED THRUST PULSE JET PUMP OR MOTOR AND METHOD OF CREATING AUGMENTED THRUST OR SUCTION Filed June 6, 1950 E l1 Sheets-Sheet l0 1 an @E f Of/V JNVENToR. FHV /VUL Nov. 17, 1953 F. E. NULL 2,659,202

AUGMENTED THRUST PULSE JET PUMP ORMOTOR AND METHOD OF CREATING AUGMENTED THRUST OR SUCTION Filed June 6, 1950 ll Sheets-Sheet l1 BY U1-6L...

Patented Nov. 17, 1953 UNITED STATES PATENT OFFICE AUGMENTED THRUST PULSE JET PUMP OR MOTOR AND METHOD OF CREATING The invention described herein may be manufactured and used by or `for the Government for governmental purposes without payment to me of any royalty thereon.

This invention relates to an augmented pulsejet pump or motor of the kind'in which a combustible gaseous charge is exploded to form a jet of hot gas and the jet is used to entrain air to build up a substantially continuous -current of gas of greatly augmented mass. This current of mixed products of combustion and a large excess of air can be used to change the air in buildings by the process of exhaustion, to produce low vacua, to increase boiler draft, to act as an indirect or direct heating means or to propel aircraft or marine craft.

'in my pump or motor, the air from a rotary compressor is premixed with fuel vapors and then enters the ring chamber through a rotary slide disc valve in the presence of an easily detonated vapor near a row of spark plugs. The charge is exploded by a high velocity shock wave from the detonating vapor, and the explosion is so rapid that only a small amount of vapor leaves the open end of the firing chamber during the explosion, which occurs at approximately constant volume. This action causes a maximum pressure and temperature and makes possible a high thermal eiciency. The combustion products expand rapidly in a ared tube to a supersonic velocity; a shock Wave with a sharp front edge leading the expanding slug or gas column. As the shock front overtakes the still or loW- velocity air in front of it, this air is greatly com-- pressed and added to the slug ofl combustion products and air. The combined gas and air slug has a high velocity which is determined by the equations of normal shock, the velocity of the air being less than that of the shock front. The pressure on the upstream side of the shock wave must be different from that at the rear of the slug of combined gas and air by the rate of change in momentum of the column. The volume of the slug is determined from the gas equation from the average pressure and temperature of the known mass of the slug. As the slug moves down the tube, its momentum causes the production of a partial vacuum behind the slug which sucks in air through valves along the sides of the flared expansion tube. Therefore the slug is followed by a column of air flowing in at a fairly high subsonic velocity. valves have no moving parts, but consist of vanes and ducts so arranged that the peripheral portions of the'slug start a typical Prandtl-Meyer The lateral filling.

sec. 266) expansion around the corner of the valve openingbetween the expansion tube and low pressure chamber. A special guard vane is employed to separate the peripheral flow from the main flow in the expansion tube. The upper surface of this guard vane is shaped to reect the expansion waves incident upon it from the corner of the valve opening to an outer vane the tip of which is approximately tangential to the stream cf eX- panding gas and which is curved to lead back to the expansion tube proper. The formation of oblique shock Waves along this outer vane is prevented by the incidence of the reflected'expansion waves, which cancel out the oblique shock waves which would otherwise form along this surface. When the peripheral portions of the'gaseous slug reach the valve opening to the low pressure chamber, Vthey ow in a typical Prandtl-Meyer expansion around a corner until they reach the reflected expansion waves which deflect the ow back toward theexpansion tube. The flow pattern is somewhat different for the front and rear portions of the slug, which travel with different velocity. However, a smooth flow results in each case, with the formation of only weak shock Waves and with a small turbulence loss. When the low pressure tail of the gaseous slug reaches the lateral valve openings, air from a low pres-1 sure chamber ows in to ll the expansion tube. The low pressure chamber surrounds the expan sion tubes and has a turbine at the front air entrance. As the air from the chamber rushes into the expansion tubes, the pressure in the chamber is decreased. Air entering the chamber drives the turbine which is geared to an air compressor which supplies high pressure air to the firing chambers for combustion of the fuel. Before one slug of combustible gas and air reaches the end of an expansion tube, a succeeding slug has been fired and its front has collided with the rear end of the preceding slug, thereby compressing it, and causing the output pressure and the velocity from the expansion tube to be fairly constant. Small pressure variations are present, however, and have the same frequency as the slugs red in a given tube, i. e., several hundredv per second in an expansion tube l5 feet long. The flow of air into the low pressure turbine chamber may be used as an exceedingly fast large volume suction pump for exhausting air and fumes from buildings or for commercial processes requiring a vacuum which need not be constant. The exhaust streams from the ends of the expansion tubes may be used as an exceedingly fast, large volume ejector pumping means for forced draft on boilers and commercial processes where a small percentage of combustion products in air is of small importance, or for indirect heating systems. Because of the initial high pressure and temperature of the combustion products the thermal ecien'cy is fquite high, fand 'such an augmented jet of gases furnishes 4an 'efficient means of aircraft propulsion for speeds up to 300 to 400 miles per hour. Because of the non-turbulent augmentation of momentum wh-ichis possible with a pulse jet engine, -a-small `:massof very high velocity gas produced with high thermal ef ciency is changed by my device with high mechanical efficiency into a very much larger mass of low velocity, relatively low pressure gas. The ratio of the thrust produced by the large gaseous mass M, which is a low velocity exhaust jet, over that produced by the original .high pressure, high velocity, small gaseous mass m' without augmentation, is \/M/m. It :has been found impractical to produce eicient augmentation of the momentum Aof Va jet by adding 'air Vto a steady flow .of Vgas dov/ing .at appreciably different velocities without excessive turbulence .along 'the boundary line. The normal shock waveiproduced in an expansion tube by the expanding gas slug impacting on 4the slower moving air Win front of it, reduces the momentum gain ratio to 'about 87% of the vtheoretical.no-shockloss value, when the exit velocities 'havebeen .reduced to several hundred feet per second. The momentum Vaug-- mentation of the pulsejet is therefore, however much higher .than for a -j et'with steadyflow.. The .cost of fuel for the above pump is decidedly less than the cost of electricity Vfor a .motor-compressor unit of the same capacity. In addition the volume, weight, and original cost arevery much less for the -pulse je't pump or motor described above. In .the case of :an indirect heating system with forced draft, the eiliciency is still higher, as the mechanical energy loss due to the shook wave in the expansion tubes is converted into usable heat. vSuchadditions or m'o'dications may be made without departing .from the spirit of this invention.

It is therefore among'the objects of the present invention to provide a very .high capacityvalve controlled pulse jet pump 'ormotor'that maybe used for vacuum, pressure, 'vacuum 'and pressure simultaneously, or forpropulsion, 'and whic'hha's the advantages of small Weightloss 'licor space, lower initial cost, and lower operating coststhan the conventional electric motor 'and centrifugal or axial ow compressorunits.

'More specifically, .one 'object .of .the invention is to `obtain high thermal eiciencyby an explosion occurring at constant volume 1in a #firing chamber, vthe vexhaust end of which is open and which leads .to an expansion'tube, bythe vaction of a detonatingshockwave'from a detonatable mixture admitted to the 'edge 'ofthe'i'iring 'charnber nearspark plugs or otherignition'means.

Another "object of `the invention .is to l provide a'pulse jet pump or'motor'having a rotarydisc valve which gives positive "control to the admission of a premixe'd air and'fuel vapor'mixture `to the ring chambers.

Another object of the invention is vto provide a pulse jet 'pump ormotor having air inletvalves to the expansion tubes having 'no 'moving parts, such'valves beingadapted to prevent the escape of high pressure, highvelocity gas .or air vfrom the sides 'of .the expansion 'tubes as the compressed piston onslug of gas andair'froma given explosion pulse travels toward `the mouth of'the expansion tube. Such valves, however, allow air to enter the expansion tubes by the action of the partial vacuum produced in the wake of the slug of gas and air as it travels through the expansion tube.

Another iob'ject .foi the invention 'is to :provide ln a `jet pump or "motor, 'means to transform the small mass, high velocity jet from the firing 'chamber into the low velocity, but much larger lmass vleteprod-uced at the exits of the expansion tubes Zby the passage of the normal shock wave front which leads fthe initial slug of high velocity gas discharged from the ring chamber and which compresses the lower velocity air in its path, .this compressed air adding to the mass and volume of the high velocity slug of gas so that theLga'seous slug grows in mass as it passes along nthe expansion tube.

Another object of the invention is to provide in a jet pump or motor, a low pressure chamber partially evacuable by valves leading to expansion tubes, 'and Yhaving a -turbine driven 'by the gair which enters the low pressure chamber. This turbine'isadaptedto drive a compressor to compress combustion air which isthenpremixed with thefuel'vapors and admitted to the firing chambers through rotary valves,

VAnother object of the invention is to provide in apulse jet'pump or motor, an .adjustable firing-frequency m'ea'ns so `that before a 'slug of compressed vair and A.gas Vfrom one shot clears the .expansion Atube,it is impacted from the .rear by the head 'of the `slug of Vcompressed air .and gas from -a 4succeeding shot, the high pressure head of the succeeding slug compressing the low pressure'tail 'of the preceding slug, .and providing a more uniform pressure and velocity of the exhaust from the expansion tubes.

Object Aand advantages other vthan those ,above set'forth "will 'be apparent to thoseskilledin the art from "the .following description when read .in connection with the accompanying Ai:lrawir1gs,.in which:

gig. lis a front elevation taken from the inlet en .Fig 2 is a side elevation, `the internal Lparte beingshown'in dashe'dlines;

-Fig "3 Ais ian elevation .of the invention .taken fromithe .outlet end;

Fig. 4 isa sectional view inside elevation A*of thelpump or motor with the case cutaway from the rear portion, .and .the case vcutaway from .the front portion to :s'howa vertical section .through line '4-14 inFig.1;

liigs. I5 and 6 are vperspective 'longitudinally broken-open views .of my .new pump or .motor taken .cutward'from .theline '5i- 5 .of Fig. 4 views 5 zand f5 tare 4`to .be .taken-together, Fig. r6 .formingaa continuation of Fig. 5. The latteris shown partly exploded at the compressedair feeding means ,to show .in phantom how .the hollow .axle fits .into the `rotary-A ir .feed .and .the Yholes through .which airentersand leaves theaxle. .Fig showsthe centrali-supporting -tube .broken away, f also .one l-oi the .expansion .tubes vexploded .to show Vits internal construction;

Figi?? jis the .enlarged v portion vof rthe horizontal section vthrough-the .central axle indicated bythe line '1 -7 of Figs. '2 `and 5 in vthe vicinityofthe valvetolvtheiing chambers;

`Figs. 1.8, 9, lll), 1'1'1 and L12 are vertcalsections of 'the valve region shown .in lig` 7, the sections being' taken .onlines 8-.8 .to `l2-|.2, respectively;

Figs. `l3 .and 213e .show horizontal .sections :for twogpositions of .the valve shown in .Fig.`7

Figs. 14 and 15 are schematic diagrams ofsuc cessive flow patterns in anexpansion tube. Fig. 14 shows the action of the inlet valves when the pressure in the expansion tube is greater thanA that in thesurrounding chamber. Fig. 15 shows the action of the inlet valves Ywhen the pressure in the expansion tubes is loweredin the wake of a slug of gas and air passing down Va tube;

Figs. 16, 17 and 18 show the positionsof compressed air slugs in the expansion tube in different phases of the firing cycle. Fig. 16 shows the initial slug of compressed air, Fig. 17, the overtaking of the first slug by the second, and Fig. 18 the overtaking of the nth slug. by the n+1-slug after steady conditions have been reached;

Fig. 19 is an enlarged schematic View of an inlet Valve with typical expansionwave reflections for the rear of a slug traveling at relatively klow supersonic velocity. Fig. 19a shows the same valve as in Fig. 19 but for the relatively high supersonic Velocity of the front of thel slug of compressed air and gas;

Fig. 2O showsthe vertical section of a supersonic jet expanding from an orifice into a region of lower pressure;

Fig. 21 is a portion of an enlarged vertical section along line 2I-2I in Fig. 13 and extending across the edge of a horizontal ring chamber;

Fig. 22 shows an elevation of the bottom :firing chamber of Fig. 4 with a portion of one wall removed to show the spark plugs in the lower portion, with a vertical section of the adjoining valve wall;

Fig. 23 is a Vertical section along the line 23-23 in Fig. 22;

Fig. 24 is an enlarged detail of the vertical section of a spark plug in Fig. 22;

Fig. 25 is a schematic wiring diagram of the automatic controls for the present invention;

Fig. 26 shows a graph of operational characteristics;

The above figures illustrate a special apparatus embodiment of the present fundamental invention. The following Figs. 27 through 30 illustrate another special embodiment of the fundamental process.

Figs. 27 to 3() inclusive are diagrammatic representations of a flaring tube provided with a valve at the beginning of the are. Successive cyclic phases are indicated, the Various conditions and kinds of gases in the tube being shown by different kinds of hatching, legends being provided'for the purpose of identifying the gases. The invention illustrated by these figures is a special method of operating an augmented pulse jet engine, as distinguished from the fundamental general method illustrated in the remaining figures as follows:

Figs. 31 through 33 illustrate different phases of the fundamental process. Fig. 31 shows the Explosion Phase, Figs. 32 and 32a the Impacting (Augmentation) Phase, and Fig. 33 is the Augmented Delivery Phase.

Referring more particularly to Fig. 1, the blades of turbine I are driven by air flowing into the low pressure chamber 2 (Figs. 2 and 3) which surrounds the expansion tubes 3. 4 is the inlet to the compressor 5 from which compressed air passes through vane slit openings 22 in the disc of the turbine I (Fig. e) to the air-fuel premixing chamber 6, air-cushion feed l, rotary disc Valve 8, firing chambers 3, and expansion tubes 3. After the ring chambers 9 have been filled with a premixed charge of air and fuel and an air cushion next to the valve, the valvecloses, the

charge is fired, and a slug or piston 41 (Fig. 161)., of high pressure, high velocity gas and air expands down the expansion tubes 3. Due tothe momentum of this high Velocity slug, a low pressure area follows in its wake and air from. low pressure chamber 2 rushes into the expansion tubes 3 through valves Ill. This lowers the pres,- sureV in chamber 2 and 'external air rushesin throughduct opening II (Figs. 2 and 4),'.part of the flow being bypassed around the turbine Iby variable length cylindrical vane i2. The velocity of the air going throughthe `turbine determines its speedand thereby largely the speedv of the entire motor. f The turbine i drives theair compressor 5 through a conventional gear box'in the container I3 which also contains'a conventional starter motor (not shown) and electronic control equipment which willbe explained later. inconnection with Fig. 25. The container I 3k iscar.- ried by a support I4, which also mounts the front end of the main axle I5, the other end of the axle I5 being carried by a support I6. The supports I5 and I3 are mountedv on a base il which also supports an outer shell I8 which forms the outside surface of the low pressure chamber 2 and has a semi-rounded rear end Ia enclosed except for the mouths I9 of the expansion tubes 3. The internal structure is supported inside the cylindrical shell by members 25. v L

Fig. 4 illustrates the flow system of the pulse jet pump.' External air enters the ducts 4 to the centrifugal compressor .15, into passage ZI, through vane slit openings 22, past fueljets 23', supplied from pipe system 5d through turbulence-inducing meshes 24 in premixingv chambers 3, around baiiies 25, through opening 261 into passage 2l, where if the rotaryarm air cushion feed `I is out vof the way,y the premixed charge passes through duct 27a, valve 3 when open, and

into firing chambers 9.- Other compressed airin passage 2| passes through valve slit openings 23 in the blade disc of turbinek i, past detonatingfuel jet 29 through turbulence-inducing screens 30 into annular chamber 3L' and if the rotary arm of the air-cushion feed `I is out of the Way it enters duct 32 and through valve 8 (when open) so-that the premixed detonating fuel is foundin the section 9o, `of lthe firing chamber 3. 'As soon as the main portions of the firing chambers 3 are nlled'with premixed fuel and air and the `region 9a is iilledwith the premixed detonating'fuel and air at the edge ofy the firing chamber next to the spark plugs 35y (Fig. 22), .the arms of theair cushionfeed 'I close the entrances to-ducts 21a and-32,and allow `a cushion -of compressed air to flow through valve 8 Vjust before it closes, ready for firing. The compressed air for the cushion air feed'I has come from holes 33 inthe hollow axle I5 supplied from holes 34 from the passage 2|. Fig. 22 shows a vertical section of the edge of the firing chamber containing lthe row of spark plugs 35. The alloy steel walls 35 and 31 (Fig. 23) form a-cooling jacket for the circulation offuel around the ring chambers 9 before it is forced out of jets-23; The-inner surfaces `of 4the ringchambers 9 are lined with a-'thin layer 'of refractory material 38 such as a ceramic. t

Fig. 24 shows a vertical section of a spark plug 35. The electrodes 39 are mounted in a refractory insulator 40 such as porcelain which is recessed below the surface of the firing chamber Wall 36 to form a protecting pocket of air not swept out by the filling-fuel and air mixture, and are cooled by theiiow of fuel from tubew4I and that iiows out through tube 42, the fuel linesand actuaba A.electrical connections being brought to the vfuel chambers 9 through the .conduits 44 and 43 in Fig. 4. The special fuel-air mixture (such as .air and acetylene or methane) in the vicinity of the spark Aplugs is detonated by the line of .spark plugs 35, and a high velocity combustion shock wave travels laterally across fa firing `chamber so rapidly that lno -appreciable amount of the combustion products can 'escape through throat 68 into an expansion tube 3 during the explosion, which thus occurs `at constant volume with the maximum pressure and temperature required for a high thermal eiioiency Ain any heat engine. The compressed air admitted through valve 8, just before it closed, by the air cushion feed arms l, acts asa thermal .barrier to protect the rotary disc valve 8 from the full .heat of the explosion. After the firing of chambers 9, slugs of .high pressure, .high velocity combustion products escape into the expansion tubes 3, and impact against lower velocity air in the expansion tubes 3 with supersonic velocity. The 'fronts of the slugs 4l of combustion gases are normal shock waves that compress the air that they overtake and add it to the high velocity slug of combustion products, which travels Adown the combustion tubes 3 at a. velocity somewhat less than that of the shock fronts. The inlet valves I to the expansion tubes 3 have no moving parts and their detailed action is illustrated in Figs. 14 through 18. For the .illustration of the general ow pattern it is suiiicient to note when the head of a high pressure, high velocity slug of gas and air passes a valve I0, it starts to expand and deflect toward the openings (Fig. 4), but is intercepted by I outer vanes 46 and directed back into the expansion tubes 3. After a high velocity slug 41) to 41h has passed, its momentum produces a partial vacuum in its wake, and air rushes into expansion tubes 3 through openings 45 from the low pressure chamber 2. The front of the slug 4'I'f is shown as having overtaken and combined with the rear of the preceding slug 48h, producing a.4

nearly steady pressure and velocity exhaust from the mouths I9 of the generally pyramidal expansion tubes 3, The succeeding high velocity slug will in turn compress the air that is pulled into the expansion tubes 3 in the wake of the slug 41T to 41h. The reduced pressure `in chamber 2 'causes external air to flow in air ducts I I. The amount of air ow through the turbine I is regulated by variable length, telescoping cylindrical vanes i12, the position of the outer one being determined by a cable 49 one end of which is attached 'to the inner edge and one end to the outer edge of the extended cylinder. The cable 49 is driven by drum 50 on servomotor 5I. YStationary vanes 52 direct the air through the turbine vanes 53. The .turbine I drives the centrifugal compressor 5 through conventional gears (not shown) in box I3.

For detailed consideration of rotary valve yil and air cushion feed I, preference is made to Fig. 5 and to Fig. '7, a horizontal section along line AfI--l in Fig. 2 vor Fig. 5. The main axle I5 mounts the arms of the air-cushion feed 'I 'which 'secures drum rim to carry a disc valve 8 as it slides between plates 56 and 51. The disc valve 8 is thin and flexible so that perfect alignment is not required over an extended surface, it being kept taut by an inner ring 58 which is bolted to the inner edge of the disc. The disc valve 8 rotates in ball bearings 58a which lie in vgrooves 59 in the much thicker plates 56 and 51. these being attached to a stationary tube 60 which is carried by the 'supporting plate :6L Valve B is shown open to allow flow of `gaseous charge into the iiring chamber 9. Valve B is 4shown closed in Fig. 2l which .is a horizontal section along :line 21h21 Fig. 13. Figs. 13 and 13a are'the same as Fig. 7 except that they show one closed and one :open position respectively tof valve 4i, withe out Iinterference from the airfeed arm 1. The duct 21a leads to the duct B3 ina plate 56 and to the 'duct 62 in plate 5.1 which acts as the head vof the rectangular cross Vsection rin'g chamber 5 with its `fuel cooling jacket @It Rollers 64 .prevent the vexcessive wear that would otherwise occur if the 'edges il were deiiected linward by the pressure against y'an edge of duct t2 or t3. The edges L61 may `be set .for the desired small clearance at the ducts 63 and 62 by 'adjustable bearings 64a (Fig. 7.), before the assembly of valve 8, by nrst adjusting the rollers 64, the bean ings 64a of which are mounted in the plate 51. The disc of valve 8 is moved against the .rollers 64 by sliding the drum rim 55 to the right. Rollers 64 (mounted on bearings 64a in plate 56) lare then adjusted against the disc 'of valve 8 by sliding plate 56 and projection 69 'over the tube 60 `and support I0 respectively then locking projection '69 to support ID by conventional means. Oil pressure feeds 65 (Fig. 2l) provide a vcontinuous oil film which with the small clearance of the rollers 64, prevents after an explosion the 'escape of appreciable amounts of the high pressure air cushion compressed in the head 62 of the ring chamber 9. As the head 62 and firing chamber 9 are 'very narrow, the high strength alloy steel valve blade of valve 8 is not bent suicien'tly into the duct 53 to exceed its elastic limit. The thermal loss to the cooling fuel jackets 66 is not high because the combustion products only remain in the ring chamber 9 for a few thousandths of a second, the combustion products passing from the throat 68 (Fig. 4) into the expansion tubes 3 (see Fig. 46) at whatever the velocity of sound may be for the elevated temperature at 'the throats 58. The cylindrical bottom 69 of duct 21a is supported by the disc I0 mounted yon the tube BIJ.

In Fig. 6 is it shown that there are preferably four expansion tubes 3 held concentrically with in the shell i8 and surrounded by the low-pressure 'air space 2. The vmounting or spacing mem bers for the tubes 3 are 2i] while their combustion chambers are supported by extensions of the plate Si. Plates SI and Ita support a. hollow tube te 'which does not revolve. It is coaxial with the axle It, which however, is too short to contact the tube et. Within 'the double walled combustion oriring clrarnbers Q, the roiw of spark plugs 35 are seen to extend. The electronic controls, vincluding the ignition current supply is housed Within the boxes E atone side of the flaring rectangular outer ends of the expansion tubes 3. These ends are supported in apertures in the plate Ita. A row of six inlet valves I5 formed in part by outer vanes 4E is shown for illustration only.; these valves may `have a fior-m modified from that shown or may be present in adiierent number.

The valve S and air cushion feed l' are shown in greater detail in Figs. 8 through 13.

Fig. 9 is a vertical section along line 9 9 in Fig. 'i' and shows the four entrance ducts 5E to the four ring chambers t, the support SI, the expansion tubes 3 and the infiowing 'air 3a along their sides in dashed lines. The four blades of .rotary valve 8 are 'shown to one side of the yfiring chamber entrance ducts 62 .corresponding to the open position of the valve 8. The blades 7i are drawn taut between thedrum rim 55 and the ring B which slides in groove 59 (Fig. 4) in plates 5E and 5l which are supported by the tube 6G and support 5I.

Fig. 8 is a vertical section along line 8-.8 in Fig. 7 and shows the four ducts 53' in the plate 5S, the rotating rim 55 separated from the xed plate 5t by the annular space 73. The end of the ring 58 is shown in the groove 59, plate 56 being supported by tube 5B.

Fig. 10 is a vertical section along line lll-IB in Fig. 7. The rotating drum 55 is separated from the stationary plate lll by the [annular space 13. The ends of the four ducts 21a in the plate le' are extensions of the four ducts 63 in the plate 56; plate 'M being supported by the fixed cylinder 69.

Fig. 11 is a vertical section of the air cushion feed-7 along the line il-Il in Fig. 7. Mounted on the axle l5 is the disc l5 which forms a back wall for the inner portions 15 ofl the four air feed arm channels ll that receive compressed air through holes i8 and outer parts 1S of which slide on the face plate ld. When the air feeder arm channels 11 are opposite the four ducts 21a, compressed air ilows through the feeder channels l'l into the ducts 21a. At all other times the premixed charges of fuel and air in chamber 2l, and the premixed charge of air and detonatable fuel in chamber 3| are free to flow intothe ducts 21a leading to the valve 8. The outer ends of the channels 17 are secured to the edge of the rim 8H which supports drum rim 55.

Fig. 12 is a vertical section along line l2-I2 in Fig. '7. The outer rim 8D of the four rotating arms of the air cushion feed 1 support the drum rim 55. The edge of the wall 8i of the lowpressure chamber 2 makes sliding contact with the rim 55 (Fig. 7). The inner ends 'i6 of air feed channels l? are attached to plate 'l5 and receive compressed air from axle I5 as shown more clearly in Fig. 7. The outer parts 19 of compressed air feed channels 'il ride over plate lll, and supply compressed :air to ducts 21a when they pass over them. Y

Figs. 13 and 13a show horizontal sections of two different phases of the valve 3 of Fig. 7. In Fig. 13a the valve 8 is open and the air feeder channel ll is not covering the ducts 21a, so that premixed fuels and air pass from passages 2l and 31 in Fig. 4 into the ducts 52 that form the heads for the ring chambers S. In Fig. '7 the air feeder channels 1l have covered the passages 2'? cutting off the supply of premixed fuels and air, and supplying compressed air into ducts 21a, and through valve 8 to ring chamber heads t2. In Fig. 13, valve 8 has closed ready for the firing of chambers 9, and the air feeder channels l1 have cleared the ducts 210;, allowing premixed fuels and air again to flow into ducts Zla prepanatory to the opening of valves 3 for the next firing cycle.

Figs. 14 through 18 are schematic drawings to illustrate the action of the valves l0 (Figs. 2 and 4) that prevent the escape of the high pressure, high velocity air and gas slug from theexpansion tubes 3 into the low pressure chamber 2, but when the pressure in the expansion tubes is reduced in the wake of a slug of gas and air, allow free flow of air from chamber 2 into the expansion tubes 3. As the inlet valves are symmetrical with respect to the two long sides of the and feeder 1 fcrosssection of thevexpansion ltubes 3, only one ing the surface of outer vane 84 approximately tangentially. Outer vane 84 is curved in the direction to deflect the flow back into the expansion tube 3 with the normal cross section at the next valve corner 82. The specially shaped surfaces l02a and |0211 (Fig. 19a) of guard vanes 8B are designed to reflect expansion waves from corner 82 to the surfaces of vanes Sil and thus prevent the formation of oblique shocks that would otherwise occur at this surface. At the corner B2 the air flow has been slowed to subsonic velocity, and no shocks can be formed. The outer vanes 8d are shaped to be tangential to the flow expanding across the openings 8'! in the subsonic inlet valves Ib, so: that a` smooth ilow is obtainedwithout undue turbulence.

Fig. 15 shows the air in low pressure chamber 2 rushing into expansion tube 3 through valves l0 to lill a low pressure volume in the wake of a compressed air and gas slug. The air as indicated by arrows 88 enters at only a small angle to thewall of expansion tube 3, and at the valve Illa nearest the firing chamber ii the flow may temporarily be toward the ring charnber as indicated by arrow 89.

Fig. 16 shows an initial slug of gas and air 411 with normal shock front F1 still traveling somewhat above sonic velocity into the still air ahead, although the air and gas on the left, high pressure side of the shock front F1 travels at a velocity greatly below transonic values. The same pressures and relative velocity would exist if the front F1 were stationary and the air on the right were approaching it at the supersonic velocity V1 not very far above sonic value. After passing the normal shock point the air velocity would be reduced somewhat below the sonic value, but would have a relative velocity to the stationary front F1 of nearly sonic value. Hence the relative velocity of the front F1 actually moving with greater than sonic velocity 'must be in the neighborhood of the velocity of sound, or the velocity of the air on the high pressure side of the shock F1 must be a relatively low value as hundreds of feet per second. The pressure P1 on the left of the shock front F1 may be very high compared to P0, the atmospheric pressure for the still air ahead. The rear of the slug 411 is not sharp as indicated by R1 for the purpose of illustration, but is somewhat diffuse, although the bulk of the gas and air once belonging to the slug can be contained within two boundaries such as F1 and R1. The shock front F1 can only exist for a definite set of pressure, density, and velocity ratios of the fluid on its rear and front sides, The pressure P1 must also equal the static average pressure inside the slug 41 as given by the equation of state plus the pressure produced by virtue of the rate of decrease of momentum of the slug as its velocity decreases from impacting the still air ahead. The pressure P1 at the rear of the slug 471 has a pressure equal to the average static value minus the change in pressure produced by the rate of decrease of momentum of the slug. There is a pressure gradient from the front to rear of the slug. Thus the portions Y13 portional to the pressure measured by plckoff |83 in expansion tubes 3.

Section E.-Pressure correction circuits to regulate the frequency of reference oscillator |43 to a value to maintain the output pressure at the desired reference value.

Section F.-To keep the speed of the fuel pump motor proportional to the reference and firing frequencies.

In the schematic circuit drawing of Fig. 25 in section A, a pickoif wheel |2| is coaxial with the blades of the valve 8, and is contained in the auxiliary box I3 of Figs. 2 and 4. Valve 8 has just closed the duct 62 (in Fig. l0) to the firing chamber 5, and the spoke |22 (Fig. 25) of the test pickoif wheel |2| has just interrupted a light beam |23 from a light source |24, which beam is prevented from reaching the photoceli detector |25. Thus, when the firing chamber 3 has been charged with an explosive mixture through duct 62, and the valve 3 has closed ready for firing, the interruption of the light beam` |23 by the spoke |22 suddenly stops the D. C. current fiow in the primary |26 of transformer |2'l which is in series with a self-generating photoelectrio cell |25. The sudden stoppage of D. C. currentl in the primary |23 produces a voltage pulse in the transformer secondary |28. The current pulse produced in the secondary |25 is of the correct polarity when the light beam |23 is interrupted to flow through the rectifier |25. On the contrary, the current pulse produced in the secondary |28 will not be of the proper polarity when the beam 23 is uncovered by the spoke |22, thus preventing sparking except when the valve 8 has just been closed. A resistor |33 is in series with the rectifier |29 and the secondary coil |28, and the voltage across it is impressed on an audio amplifier 3| which is tuned approximately to the fundamental of the pulse from resistor |33.

The output of an amplifier |3| is in series with the primary of a transformer |4| and an input thyratron |32. The thyratron |32 is in series with the primaries of transformers |34 and |35,

and a condenser |35 which may be charged by a D. C. source |36 through a small fixed resistor |31 and a tube |38. When a voltage pulse is received from the amplifier |3| on the input of the thyratron |32, the thyratron |32 fires and discharges the condenser |35 through the primaries of transformers |34 and |39. Such action causes a ring spark for chamber 3 to appear at gap |46. In order to measure the firing frequency by an integration process, it is necessary that the voltage pulses across transformer |34 all be alike. This is partly achieved by designing transformer |34 so that its core is saturable at each pulse, but since the knee of the magnetization curve is never really sharp, it is in addition necessary to insure that the condenser |35 is charged very nearly to the saine voltage before each discharge. This requires a rapid charging rate for condenser |35, and to. effect this'result the voltage source |36 is impressed in series with the small fixed resistor |31, the condenser |35, and a variable impedance tube |33 which normally has a very low impedance. Therefore the charging rate of the condenser 35 is very rapid except for a short period at the breakdown of the thyratron |32. The pulse which res the thyratron impresses a voltage on transformer |4| that is transmitted through a rectiiier |43 to a capacity-resistance network |42 the time constant of which is adjusted to the desired short period. The voltage across this network biases the tube 38 to cutoff. Therefore the voltage from D. C. source |36 cannot prevent the thyratron |32 from reopening when the voltage on the condenser |35 normally passes through Zero because the condenser |35 is then separated from D. C. source |36 by the high impedance of tube |38. A rectifier |49 prevents a decrease of the pulse voltage from the amplifier |3| from openn ing the tube |38.

Section B of Fig. 25 has the function of producing a series of pulses of a frequency determined by a sawtooth oscillator |43 which is used as reference. The output of the oscillator |43 is connected to trigger the thyratron |44, which is in series with the primary coils of transformers |45, |46 and 264-265, and condenser |41. The transformer |45 is designed for core saturation on each pulse-discharge through the thyratron |44. To insure that the number of voltage pulses on transformer |45 can be recorded by integration of the separate pulses, these pulses are made further alike by a circuit able to charge condenser |41 very rapidly to the full voltage of D. C. source |36. Voltage source |36 is in series with alow resistance fixed resistor |49, the variable impedance tube |53, the primary of transformer 264-265and condenser |41. At the instant the thyratron |44 is fired by a pulse from oscillator |43, the secondary 265 of transformer 254--265 which is in series with a rectifier I5! impresses a voltage pulse on the latter and the capacity resistance network |52 which is in parallel with the input of tube |50. For a short period at the time of firing thyratron |44, determined by the time constantof the capacityresistance network |52, the tube |56 is biased to cutoff, thus giving the thyratron |44 opportunity to open as the condenser |41 discharges to zero voltage. The rectifier |5| allows passage of only such voltage polarity from the transformer |48 as will bias tube |56 toward cutoff.

Section C of Fig. 25 shows the circuit for controlling the turbine speed, and since the turbine is mounted on the same shaft as the valve 8, the loading of ring chambers 9 is controlled by the turbine speed. It was shown in the description of section A that the firing frequency was controlled by the speed of rotation of the blades of valve 3. It is the function of the circuit in section C to compare the actual frequency of firing pulses received on leads |53 from transformer |34 with the number of voltage pulses on leads |54 coming from transformer |45, which are equal to the frequency of the reference oscillator 43. The ming-voltage pulses from leads |53 are in series with the rectifier |55, condenser |56, and the variable resistor |51. The reference voltage pulses on leads |54 are in series with variable resistor |58, rectifier |59 and condenser |66. Resistors |51 and |58 may be adjusted to a point at which, for an equal number of ring and reference pulses, the voltages on condensers |56 and |65 are equal. The resistor |6| is in parallel with condenser |56, and resistor |62 is in parallel with condenser |63. Since the condenser voltages are of opposing polarity, the voltage to the input ampli-'- er |53r will be zero when the condensers |56 and |66 are charged to voltages of equal magnitude; the ring and reference frequencies then being equal. lf the firing frequency is different from the reference frequency, a voltage will be impressed on the amplier |63 to operate the solenoid switch |64. For this switch the center position of the armature contacterv |65 corresponds to zero solenoid current. The D. C. voltage source |69 is impressed upon the resistors |91 and |68 in series, leads from the midpoint |69 of resistors |68 and |61 and the contactor |65 going to the servomotor 5|. On the servomotor is mounted the grooved drum 50 which is wrapped by one loop of cable 49 which, as previously mentioned, pulls the cylindrical vane |2 (Fig. 11) in or out to control the air intake and speed of the turbine I. If the firing frequency exceeds the reference frequency, the contactor |95 is pulled to contact |19, and contactor |55 is then electrically negative to point |69 between resistors |68 and |61, and the servomotor drum cable control pulls the vane |2 farther forward. Less air, is thus intercepted and the turbine speed is reduced. If the ring frequency is less than the reference frequency, the contactor I 55 is pulled to contact I1 I, and the servomotor 5| is rotated in such a direction as to cause vane l2 to intercept more air, thus increasing the speed of turbine I until the firing frequency is equal to the reference frequency.

The circuit of section D of Fig. 23 has the function of maintaining the speed of the fuel pump motor |11 proportional to the firing frequency, which is kept equal to the reference frequency. As will be later explained, the reference frequency may be changed automatically to keep the exhaust pressure of the pump at a desired value. Every reference voltage pulse actuates the transformer |46 which impresses a voltage pulse on the A. C. amplifier |12 the output of which is in series with a rectiiier |13 and a condenser |14. The condenser |14 is in series with a resistor |15 and a D. C. generator |16 which is connected to the shaft of the fuel motor |11. As the voltages on the condenser |14 and the generator |16 have opposite polarities, no current will flow in the resistor |15 when the speed of the fuel pump motor |11 has the correct value for a given reference frequency; the gain of the amplifier |12 having been adjusted to the correct value in the initial calibration. Opposite voltage polarities will appear across the resistor |15 when the speed of the motor |11 is greater or less than its proper value. The speed of motor |11 is controlled by a variable solenoid |18, the impedance of which is in series with the armature of the motor |11. The posi I tion of a solenoid plunger |19 is determined by the pull of the cable |80 which runs over pulleys I8| and |82. Pulley |8| is mounted on the shaft of servomotor |83 which has opposite directions of rotation for voltages of opposite polarity on resistor |15.

Section E of Fig. 25 shows a circuit for producing a D. C. voltage proportional to the exhaust pressure in the expansion tubes 3. A tube |83 leads from the exhaust ends of expansion tubes 3 to a bellows box |84 which is divided by a diaphragm |85. A compartment |89 of the box |99 on the lower side of a diaphragm |85 is evacuated. Diierences in the exhaust pres'I sure of the expansion tubes 3 cause the diaphragm |85 to move in or out with proportional displacement. The displacement actuates a lever system |81 to slide the contacter |88 along a potentiometer |89 which is in parallel with a D. C. source |99, thus giving a voltage on leads ISI which is proportional to the exhaust pressure of expansion tubes 3.

The section F of Fig. 25 shows a circuit for changing the reference frequency of the sawtooth oscillator |43 (and hence also the ring frequency, which is kept equal to the reference frequency) so as to maintain the exhaust pressure of expansion tubes 8 at the desired value. The voltage on the leads |9| is bucked against the I. R. drop of a resistor |92 which is controlled by a D. C. source |93 and a variable resistor |94 to equal the voltage of the leads |91 for the desired exhaust pressure of expansion tubes 3. If the exhaust pressure of tubes 3 is different from the desired reference value, an error vol-tage appears across the resistor |95, the polarity of which depends upon the sign of the error and the masnitude cf which depends upon the amount by which the pressure has departed from the desired value. This error voltage is impressed on the leads |96 and upon the input of two conventional triode circuits, the components of which are connected as follows: The given error voltage Dolarity is impressed across the grid and cathode of one tube |91, and across the grid and cathode of another tube |98; the rectiers |99 and 290 preventing error signal current through grid leaks 29| and 202 respectively, unless the polarity on the grid is such as to increase the plate current. Therefore, regardless of the polarity of the error voltage, one tube will always have an increased plate current and there will be no change in the plate current of the other. The leads 296 are taken across the plate resistors 293 of the tube |91 and 294 of the tube |98 in series with a de' coupling resistor 295. When no error voltage is impressed on tubes |91 and |98, the output volt age on leads 206 is balanced out by the voltage across resistor 201 which is supplied by a D. C. source 298 through a control resistor 209. The voltage across the leads 2|9 is thus proportional to the magnitude of the error voltage regardless of its polarity, and is impressed across a resistor 2| i which forms part of the input to an amplifier 2|2 which furnishes the correction voltage to be transmitted to a reference oscillator, as later de scribed.

Extensions of the leads 299 are impressed across a grid resistor 2|4 on the input of a tube 2|5 which with a conventional circuit and con.- denser signal pickoff 2 6, supplies a voltage to the output leads 2 l1 which is proportional to the Itime differential of the input, i. e., to the time rate of change of the magnitude of the error voltage, regardless of its polarity. A rectifier 2 I8 allows a voltage to be put on a capacity-resistance network 2 9, so that the voltage on leads 220 biases a tube 22| toward cutoff with a large increase in its impedance when the magnitude `of the error voltage decreases. This effect greatly reduces the output of a tube 222 which is connected to a resistor 223, when the magnitude of the error voltage is decreasing. Since the input of the tube 222 comes from the leads |91 the voltage of. which was shown in the description of section E, Fig. 25, to be proportional to the exhaust pressure of the expansion tubes 3, and since the tube 222 is used in a conventional circuit for differentiating this input signal, the voltage across the resistor 223 is proportional to the time rate of change of the exhaust pressure of tubes 3. When the tube 22| has a low impedance, i. e., when the magnitude of the error voltage is increasing, this condition results in a strong signal on resistor 223, but when the magnitude of the error voltage is decreasing, tube 22| is biased toward cutoi, has a high impedance, and the signal across resistor 223 can be made as weak as desired. This is accomplished by the setting of the variable resistor 224 in the capacity-resistance network 2 I9.

l? The diodes 225 and 226 are connected across the ends of .the resistor 223 so that regardless of the polarity of the I. R. drop across the resistor 223, the diode on the positive end allows current to flow through the resistor 221, the I. R. drop across resistor 22`| always being in the same direction, regardless `of which diode passes current through it. The voltage across the resistor 221 is impressed across the resistor 228 which is partof the input potential .to amplifier 2|2, and represents the magnitude of the time rate of change of the exhaust pressure of expansion tubes 3. The yother component; of .the input voltage to the amplifier 2|2, is, as before described, the I. R. drop across resistor 2H, which is always of a polarity to aid that across resistor 228, and is proportional to the magnitude -of the error voltage. The combined input to the amplifier 2|2 thus consists of voltages proportional to the sum of the time rate of change of the magnitude of the exhaust pressure of expansion tubes 3 and the magnitude of the error voltage which represents the amount by which the exhaust pressure of expansion tubes 3 differs from the desired reference value. The component representing the time rate of change of the magnitude of the exhaust pressure in the expansion tubes 3 is weaker for a decreasing than for an increasing magnitude of the error voltage. The output of amplifier 2|2 constitutes a correction signal which is to be applied to the reference frequency oscillator |43. The signal value depends both on the pressure error and the magnitude of the time rate of change of the pressure. Very rapid fluctuations in pressure may occur at the start of a supersonic pulse jet pump in which the firing frequency depends upon turbine velocity. It is necessary to anticipate pressure errors before they become large, by the time rate of pressure magnitude changes. However, .the correction due to the time rate of change in pressure magnitude is blanked out as much as desired by the tube 22| when the magnitude of the error voltage is decreasing, in order to prevent -overshoot and oscillations about the zero point. In order to further prevent -overshoot and oscillation about the point of zero ccrrectin voltage, a tube 229 is provided to bias the D. C. amplifier 230 to cutoff when the magnitude of the correction voltage is less than a small value controlled by the negative bias given by the potentiometer 23| which is connected in series with the grid of the tube 229. When the magnitude of the correction voltage on the leads v2 exceeds the negative bias from the potentiometer 23|, the I. R. drop von the resistor 232 increases very rapidly since tube 229 has a large amplification. Current therefore tends to flow through rectifier 233 in the inverse direction. As .this ow is prevented by the rectifier, the input to the amplifier 230 from the amplifier 2 I 2 is unaffected by the circuit of tube 229 as long as the error voltage exceeds the small voltage on the grid of tube 229 from the potentiometer 23|.

But when the magnitude of the error voltage is appreciably below the negative bias provided by potentiometer 23|, the current .through the tube 223 is markedly decreased, and the I. R. drop on the resistor 232 is considerably decreased. Current flows through the rectifier 233, the direction of current ow through the secondary 255 as previously caused by the amplifier 2|2, being reversed, the current being of a value sufficient to bias the input of amplifier 230 to cutoff. Amplifiers 2 2 and 236 are adapted to handle D. C in order to pass a correction signal which slowly increases due to a very small drift in pressure. The output of amplifier 233 is impressed across the armature contactors 234 of switch 235, the -control solenoid 236 being actuated from leads 237 which are extensions of leads |96, and are positioned across the error voltage. lTherefore, when the exhaust pressure of .the expansion tubes 3 is greater than the reference value, the contactors 234 close the circuit on the right hand side, and if the contactors 239 of second reversing switch 238 are also on the right hand side, a voltage will be impressed yon a field coil of motor 2180 in such a direction as to reduce the reference frequency and to cause a decrease in pressure to the reference value. If the exhaust pressure of expansion tubes 3 is less than the reference value, the error voltage will have the opposite sign. The solenoid 236 of switch 235 will pull ccntactors 234 to the left hand contacts, reversing the polarity of the correction current of switch 235. If the contactors 239 of second reversing switch 238 still make contact in the right hand position, the motor 243 will now be speeded up, the reference frequency will increase, and the exhaust pressure of the expansion tubes 3 will rise until it is equal to the reference value.

The function of the second reversing switch 238 4is .to provide the correct correction voltages to the motor 246 for operating conditions that occur such that the pressure-frequency curveis a double-valued function as in Fig. 26 where points A and B both have a value of exhaust pressure equal to that of the reference. It is preferable that the operating pressure be limited to small oscillations about the point A as the corresponding operating parameters lead to a higher efficiency than for point B. It is therefore desirable to provide second reversing switch 238 and its controlling solenoid 255 to reverse the polarity of the correction voltage to motor 240 when the slope of the pressure vs. frequency curve (Fig. 26) changes sign, corresponding to a pressure be- Itween points C and B (pressure greater than the reference). The normal correction is then reversed so that the frequency will decrease and the pressure increase until the maximum at C is reached, when a slight overshoot will carry the pressure intol the region for normal operation. Reversing switch 238 is then beinggactuated by the change in slope so that the frequency will 'continue to decrease until the pressure reaches the reference value at point A. In starting the jet pump, Ithe pressure and frequency build up together, the more ring shots per second the greater will befthe volume of air sucked from chamber 2 through valves It into the expansion tubes 3. The greater the flow of air from chamber Y2, the greater will be the turbine speed for the ksame setting of the inlet vane l2. However, the ring frequency may Vreach a value for which the slugs passing down expansion tubesv 3 .are too close together for an adequate inflow of air from chamber`2 into the space between them. In such case a maximum in the exhaust pressure is reached at some point C, Fig. 26, but the frequency can still increase by reason of an increased speed of the compressor 5 and valve 8 and by virtue of a change in position of vane l2 to direct more airV through the turbine'blades. If the reference pressure desired is close to the maximum pressure C, fluctuations might drive the point of operation onto that portion of the pressure vs. frequency characteristic in which the curve has a negative slope. Supersonic flow is sensitive tovchanges in operational factors such 

